1. Field of the Invention
The present invention relates to an improved compound of a bis-type azo dye which presents a black color, dye which comprises the compound, an ink, a jet printing ink which comprises the dyes, and an ink-jet recording method using the ink.
2. Description of the Related Art
Dyes which present a black color are used not only for the purpose of printing character information, but also as a black print dye in color image printing. However, development of dyes which present a neutral black color is often technically difficult. Although researches and development for the dye has been extensively carried out, there are few dyes having satisfactory properties under the existing circumstances.
For this reason, a method has been carried out, wherein plural dyes having various types of hues are mixed to form the black color. The development of dyes which can present high-density and neutral black color by itself is the technical subject which has been presently demanded most strongly.
With the spread of ink jet printers in recent years, black dyes have become more important than before. In the ink jet printers, printing based on character (letter) information is carried out at an extremely high frequency compared with a pictorial printer of another type. Accordingly, there exits a problem that black dyes used by the ink-jet printers must satisfy conditions which are required both in a case in which the dyes are used for a black image portion of image information and in a case in which the dyes are used for a portion of character information.
The above black dyes must satisfy the following required conditions. For example, they must present a high-density and neutral black color, and they must be excellent in adaptability for ink and ink stability. It is also necessary for the dyes to have high image fastness (that is, high resistance against light, heat, atmospheric moisture, chemicals, air, various gases in the atmosphere, water and friction). Further, they must cause a little variation in hues due to a printing medium (paper), and they must have excellent dyeing properties on image receiving paper. They are furthermore required to be easily synthesized, to be available at a low cost, and to do no harm to living creatures.
Although bis-type azo dyes have been proposed as the block dyes, dyes in which partial structures corresponding to A and B in general formulae (I), (II) and (III) according to the present invention are both heterocycles, have not been known with a few exceptions. Publicly known bis-azo type black dyes have problems that they have a low density (resulting from that a molecular extinction coefficient of the dyes, which is a basic physical property value of dyes, is low), does not have a hue of neutral black (the absorption waveform is broad and light in a visible region is uniformly absorbed), and are deteriorated in image fastness.
Further, some of the black dyes may have a structure in which a harmful chrome ion exists in a molecule, which becomes a problem in the safety to living creatures.